Operational performance requirements are needed to support development of specifications for downhole motor power sections to be used for drilling hard rock during geothermal wellbore construction. Theoretical torque specifications are derived based upon a widely-accepted rock-reduction model in the literature using representative properties for typical rock formations. The derived values correspond to optimum motor performance for rock reduction at minimum specific energy and form a set of minimum requirements on output torque and power for downhole motors. Actual values should be increased to account for factors such as increased hydrostatic pressure at depth, bit wear, heterogeneous rock, and non-ideal drilling conditions.